1. Field of the Invention
This invention relates generally to improving the service installation of a bellyband seal between rotor disks in a gas turbine and, more particularly, to a method and corresponding fixtures and gages for installing a replacement bellyband in a turbine without destacking the rotor, including a compact machining fixture which can be used to precisely machine the rotor disks to accept engagement features of the bellyband, and layout tools for precisely locating the machining sites.
2. Description of the Related Art
Combustion gas turbines are clean-burning, efficient devices for generating power for a variety of applications. One common application of combustion gas turbines is in power plants, where the turbine drives a generator which produces electricity. Such stationary gas turbines have been developed over the years to improve reliability and efficiency. However, due to the long service life of modern gas turbines, some parts will inevitably need to be replaced.
One such part which typically needs to be replaced during the service life of a gas turbine is an air gap baffle, also known as a bellyband. A bellyband serves as a seal between adjacent rotor disks in a turbine, preventing the relatively low-temperature cooling air flowing through the central core of the turbine rotor from mixing with the hot combustion gases flowing past the blades in the annular combustion section outside the core. Because of the extreme heat and corrosive nature of the gases to which it is exposed, the bellyband often reaches its end of life and needs to be replaced before the turbine itself is due to be retired.
When a bellyband needs to be replaced, it is desirable to do so without destacking the turbine rotor, as destacking and restacking are lengthy procedures which cause the turbine to be out of service for a long period of time. Previous methods of bellyband replacement involve manually drilling and grinding slots in the rotor disks to accept anti-rotation devices which are integral to the replacement bellyband. These traditional methods suffer from several drawbacks. One drawback is that, despite best efforts at manual measurement of the slot locations, the four segments that make up the replacement bellyband often end up having slightly different lengths—meaning that each segment becomes a turbine-specific service part. Another drawback is that the manually machined slots in the rotor disks inevitably have a slightly irregular and non-optimal shape, which causes excess stress on both the rotor disks themselves and the replacement bellyband. These drawbacks add complexity to the service replacement of bellybands, and reduce the life of the service bellybands, both of which are undesirable.